Electrical testing system



Eea 8, 1925- 1,564,259 R. G. MCCURDY ELECTRICAL rTESTING SYSTEM Filed Deo. 30, 1921 2 Sheets-Sheet l @ya t,

ATTORNEY Dec.- 8 i925- 1,564,259

R. G. MCCURDY ELECTRICAL TESTING SYSTEM Filed Dec, 30, 1921 2 Sheets-Sheet 2 INVENTOR L' 126% my ATTORNEY Patented Dee. 8, 1925.

UNITED STATE-S PATENT OFFICE.

RALPH Gr. MGCURDY, F CRESSKILL, N EW JERSEY, ASSIGNOR TO AMERCAN TELE- PHONE ND TELEG'RAPH COMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL TESTING SYSTEM.

Application lred December 30, 1921. Serial No. 525,953.

To all whom t may concem:

Be it known that l, RALPH G. Mo- Cuianr, residing at Cresskill, in the county ot Bergen and State of New Jersey, have invented certain improvements in Electrical Testing Systems, of which the folloning is a specitication.

This invention relates to electrical testing systems and especially to a method and means for determining the existence and magnitude of unbalance in telegraph composite sets and similar networks.

in signalinr systems which are designed for 'the simultaneous transmission of telephone and telegraph signals it is necessary to insert at the terminals, for example, a network adapted to separate the telephone currents from the telegraph currents and to direct each of these currents into its individual terminal circuit. Networks intended to perform this function are usually designated composite sets. They consist usually of two branches bridged in parallel across the sides of the circuit with a condenser in each side of the circuit between the two junction points of the branches, with each side of the circuit. r)The branches bridged across the sides of the circuit consist usually of two inductances in series with two condensers. For the efficient operation of lines jointly used for telephone and telegraph signaling, it is necessary that substantially no unbalance should exist in these networks.

It is the object of this invention to provide a method and means for determining the existence of unbalance in composite sets and similar networks and to determine the magnitude of such imbalance.

This invention will be better understood from the following description when read in connection with the attached drawing, of which Figure 1 shows means for measuring the unbalance of the composite set as a whole, using the null method, and Fig. 1 shows means for making the same measurement using the comparison method; Fig. 2 shows means for measuring the unbalance existing in the telegraph branches of the composite set and Figs. 2a and 2b show means for measuring the unbalance existing between the elements of the telegraph branches; Fig. 3 shows a method for measuring the imbalance between the condensers in series with the sides of the line circuit and Fig. 4f shows an arrangement for measuring the unbalance between two composite sets using the null method.

lThe arrangments shown in Fig 1 comprise a composite set, a slide wire which constitutes the ratio arms ot' the lllheatstone bridge, a source oi' testing current and a current indicating instrument. The composite set comprises two circuits bridged in parallel across the sides or" the signaling circuit, one extending from A to B, known as the telegraph branches, and the other extending from C to D, known as the grounded branches. Interposed in the sides of the signaling circuit between the two bridged circuits are two series condensers 9 and 10. The telegraph branches extending from A to B include 2 inductances 1 and 2 in series with two condensers 3 and 4. The

junction point of the condensers is connected to ground. The grounded branches extending rom C to D include two condensers 7 and 8 in series with the two inductances 5 and 6. The junction point of the inductances in this branch is grounded. One of the telegraph legs is connected to the composite set at the point G and the other leg is connected at the point H. Bridged across oneA end of the composite set between the points A and B is the circular slide wire resistance whose moveable contact point 13 is connected with one side of a source of oscillations 14, the other side of which is connected preferably through a resistance 15 to ground. Bridged across the other end of the composite set between the points C and D is a current indicating device, here represented by the telephone receiver 11. The source of oscillations 14 may be of a type adapted to give a 'single frequency or it may be of a type adapted to produce a complex wave form. When the oscillator 14 is in operation current will flow through the circular slide wire in opposite directions from the contact point 13 and thence through the various paths ot the network to the ground X, which connects the midpoints of the two branches. 1l' no imbalance exists, the points C and D will be at the same potential and consequently no current will flow through the receiver 11. It unbalance exists in the network it will be manifested by a tone in the said receiver, but the effect of this imbalance can be neutralized by proper adjustment of the variableslide wire ratio arms 12. If the slide Wire is properly calibrated the percentage imbalance may be determined trom the location of the contact point. when balance is obtained. l

If the imbalance is 4fairly large it may be dilllcult to measure it by means of the null method described in connection with Fig-1, due to the inability to obtain a sharply defined point ot' minimum tone in the receiver 11. 11:' this situation exists a measurement may be made bythe compari-- son method illustratedby Fig. 1, ln this figure and in all subsequent figures, parts similar to those described in Fig. 1 have been given the same designating symbols.v ln Fig. 1a the receiver 11 is connected with the swinging contacts of the double throw, double pole switch 1'?, the right-hand contacts of which are connected with the points C and D of the composite set, and the letthand contacts of which are connected respectively with a high resistance 16 and with ground. rlliis resistance connected adA` justably with the resistance 15 which ac ts as a potentiometer to varj7 the current through the receiver and the resistance 16 when they are connected to it. lllhen the switch is operated toward the right the receiver 11 will be bridged across the points C and D and a tone will be produced in the receiver by current from the oscillator 111, the magnitude ot which will depend upon the magnitude or' the imbalance in the composite set. rlhe switch is then operated toward the left thereb connectino` the receiver in series between the resistance 16 and ground. The variable resistance 15 is adjusted until the magnitude of the current flowing through the receiver 11, as indicated by the tone produced thereby, is the same as when the receiver is connected across the points C and D of the network. The magnitiidey of the imbalance may be determined by proper calibration ot the potentiometer 15. ln nia-,king this test the contact 13 of the slide wire-z resistance 12 should be positioned midway/,between the outer terminals ot the slide wire resistance.

Fig. 2 shows a circuit arrangement for determining the magnitude of imbalance e2;- isting between the two telegraph branches ot a composite set. By telegraph branch is meant that partof the set in which telcgraph currents are intended to flow. Since it is desirable to measure the magnitude ot' the imbalance in this particular part of a composite set without disconnecting the other branches or elements of the set therefrom, the arrangement provides for protecting the branch to be tested from the '-eilect oit imbalance in the other parts of the composite set. 1n Fig. 2, one side of the grounded oscillator 111 is connected not only to thecontact 18 ot' the slide wire resistancev 12 but also to the variable resistance 18,

which in turnv is connected to the points C and l) ot the "composite set. By meansY oi' the switch 1"? the receiver 11 is adapted to be connected either between the points B and D or between the points and B; To protect the branch to be tested i'rom the ei'i'ect ot' imbalance in the other parts oi the set it is necessary to bring to the same potential the points fr, l5, C and l). This is done by the simultaneous adjustment o the variable resistance 12 and 1S. lilith the sii'itch 1i' operated toward the right the receiver 11 is bridged across the points B and D. rEhe resistance 18 should then be adjusted until the points l5 and are the same potential, which would be indicated by silence in the receirer 11. rllhe switch 1T is then operated towarr the lett, thereby bridging the receiver across the points A and l and the slide wire resistance 13 is then adjusted to produce theminimuin tone in the receiver. The switch 1T should then be again operated toward the right in order to determine whether the points B and l) are still at the same potential, because the adjustment of the resistance 18 may produce a slight' imbalance which might cause a ditllerence oi potential across B and D. lt' such potential exists, the resistance 18 should be adjusted again until balance exists, and then the switch 17 should be operated to the lei't in order to determine whether the points A and B are still at the same potential. Complete balance or' the network may be effected byv successive adjustments of the two resistances. he setting of the dial of the resistance 12 indicates the percentage unbalanee existing between that part oia the telegraph branch, including the inductance 1 and condenser 3, andthe part including the indnctance 2 and condenser il.

Qavshows the arrangement ot the apparatus 'rer measuring the magnitude or the imbalance between the inductances alone the telegraph branch. The circuit aro rangement ditler from that shown in Fig.

2 only in the shunting out of the ccndensers 3 and 4 by connecting the points and H to ground. The method is similar to that described in connection with 2. yEhe switch 17 is operated toward the right thereby connecting the receiver 11 across the points B and B, and the resistance 18 is adjusted until these points are at the same potential which would be indicated by silence in the receiver. The switch 17 is then operated toward the lett and the variable slide wire 12 is adjusted to give ininimiim tone in the receiver 1l. lt is desirableto determine whether there is any potential across the points B and D; after the adjustment ot the slide wire 1Q has been made. Successive :uliustments olthe two resistances should be i ade until complete balance of the network is effected. The setting of this pedance of the apparatus which is connectedI around the condensers of the telegraph branches is relatively high it is unnecessary to protect against imbalances in other parts oi the composite set network when measuring the unbalance between these condenser-s. Accordingly, the outer ends of the variable resistance 12 are connected with the terminals C and H (which are the outer terminals ot the condensers -3 and 4) and the receiver 11 is also bridged across these same terminals. Cscillations from the source 14 will be applied to the network and the variable resistance 12 will be adjusted until minimum tone is produced by the receiver 11. The setting of the slide wire is a measurement of the percentage Vunbalance vor the two condensers.

Fig. 3 shows an arrangement for measuring the imbalance between the series condensers 9 and 10 of the composite set. The outer ends ot' the variable resistance 12 are connected to the points A and B of the set, and the other ends C and D of the set are strapped together. rlhe source of oscillations 1-l is connected between the contact of the slide wire 12 and the strap connecting the points C and D. 'lhe receiver 11 is bridged across the points A and B. Since the impedance of the telegraph branches and the grounded branches of the composite set are relatively so great with respect to the series condensers their eiect upon the network may be neglected. The variable resistance 12 is adjusted until the point of minimum tone is perceived in the receiver 11 and the setting ot the said resistance is a measure of the percentage unbalance between the series condensers.

rilhe method of measuring the percentage imbalance between the grounded branches of the composite set is similar to that for measuring the unbalance between the telegraph branches as described in connection with Fig. 2. ln measuring the unbalance of the grounded branches the outer ends of the variable resistance 12 are connected across measuring the percentage unbalance between two composite sets. In this arrangement the points A and B, C and D, A and B', C and D of the two composite sets are strapped together as shown in the figure, and the variable resistance 12 and the receiver 11 are connected between the two sets in the manner there shown. Oscillations from grounded oscillator 14 will be impressed across the two networks between their respective outer terminals and ground. lf the networks are balanced there will be no dierence of potential across the receiver 11 and no tone will be produced thereby. if unbalance exists its effect may be neutralizedby adjusting the variable resistance 12 until no tone or a minimum tone is produced by the receiver.

lt will be seen that by means of the toregoing arrangements it is possible to determine the existence and the extent of unbalance existing in composite sets or similar networks as a whole, and also imbalance existing between correspondingly similar parts of such sets, which measurements may readily be made without physically separating the various branches or parts that constitute these networks. It will also be seen that the methods and means heretofore described are applicable for determining the magnitude of unbalance existing between two composite sets used in the side circuits of a phantom signaling circuit. By using these methods and arrangements the conn dition of a composite set or' a similar network may, for example, be readily determined from the test-board of the signaling system without disturbing the connections of the circuit at the distributing frame or the composite rack in the olice where the tests are being made. y

Although this invention has been described as embodied in certain particular forms and arrangements of parts it is to be understood that it is not so limited but is capable, of embodiment in other and diierent forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. The combination with a composite set having two similar grounded branches constituting two arms of a VVheatstone network of a variable resistance connected with one end of the said composite set, and constituting the two ratio arms of the network, a current indicating device connected with the other end of: the composite set and a grounded source of varying potential connected with the contacter of the said variable resistance.

2. The combination with a composite set constituting two arms of a Wheatstone network of a variable resistance connected with one end of the said composite set constituting the two ratio arms of the lVheatstone 5. The combinati having tivo siniiier anches coi I two arms of zi Vifhezu. one network, of e eource of zitern current connected with :ci comp therewith, and :i euri t indicating device responsive to any nnezihince currents through the seid branches.

rEhe combi rh zi, eomgoerte set having two sini branches o'- vernihie resistance ratio arms with the seid brnnohes con i-ihcetetone network, e source ot ammmiing current connected with the seid nerr.' and a4 cierrent indicating,` device resp@4 ne to any imbalance currents iowing` through the seid. branches.

The combination with e composite set comprising an impedance in series with each side of the said set, and an impedance in shunt therewith to ground of Variable ratio arms connected with each side of seid' com-positie :L eonree of alternating potentiei Connected with the seid ratio arms, and an indicating` device bridged across the sides of thel seid set whereby imbalance between the said sides may he determined.

6. rEhe Combination with :t composite set comprising impedance in series vit-h each side oi the said set and impedance in shunt ti'ierewiti'r, of variable ratio arms bridged across theV sides of the said set7 a som-'Ce of alternating' potential ei'eetively connected with the seid varhrhie retin erins end the seid impedances, end' an indicating device connected across the seid series impedanees whereby unha-ienne between the sides of the seid composite set may he determined.

7. vrlhe combination with e Composite set comprising an impedance in series With eheh eide of the seid set and an impedance in shunt therewith to ground, Variable retio arms bridged :across the sides of the seid set, a source of eiternating potentiaiL conneet-edv with the said' arms and grounded through e potentiometer, an indicating device, and switching ineens to connect the seid device either across the sides of the said set or across said potentiometer.

ntestimony whereof, I have signed my name to this specification this 29th day of December 1921.

RALPH G. MCCURDY. 

